Wireless alarms being rubbish is largly a rumor generated by installers that dont know how to fit them.
If you buy the correct equipment and install it the right way (don't point a PIR at a heatsource for example) wireless are no worse than wired detectors. The advantage with wired is that a larger range is available that allows you to finetune the detectors to the situation.
There are some rubbish wirefree systems though, that don't warn of low batteries, radio interference, supervision problems etc. Like everything else you get what you pay for, the British Standards split radio alarms into 6 sub catagories. Only grade 6 is suitable for police response and so is considered reliable. It also complies with the new EN level 2 requirements following risk assesment. It is however very difficult to get hold off diy.